Phase responsive control circuit



Patented Dec. 7, 1948 PHASE RESPONSIVE CONTROL CIRCUIT Joseph G.

Beard, Haddonfield, and Robert W.

Harralson, Masonville, N. J., and Alexander Kreithen, Philadelphia, Pa., assignors to Radio Corporation of America, a corporation of Dela- Ware Application December 30, 1944, Serial No. 570,707

This invention relates to a phase control system I and particularly to a method of and means for maintaining two alternating signals in .phase quadrature.

Among the objects of the invention is the provision of an improved phase detector and particularly of a method of and means for detecting any change in the phase relation of two signals which are normally in quadrature.

Another object is the provision of an improved phase control system and of sensitive accurate speedy and compact apparatus for maintaining two signals in quadrature,

According to the invention these objects are achieved by producing a pair of alternating currents which are balanced when the signals under control are in quadrature and by utilizing energy under the control of an unbalance of these currents for returning the signals to the desired phase relation.

In the accompanying drawing Figures 1a and 1b are vector diagrams which illustrate the operation of the invention,

Figure 2 illustrates an application of the in- I vention, and

Figure 3 is a circuit diagram of an embodiment of the invention.

In Figure 1a two signals in phase quadrature are represented by the vectors E1 and Ea and their vector sum by the vector E111. E1 and E3 are the signals whose relative phase is to be controlled or indicated. A third signal is represented by the vector En. This signal has an absolute magnitude at any instant equal to that of one of the before-mentioned signals, say E1, but of opposite phase to E1. The vector sum of of E2 and E3 is seen to be the vector En. As long as the angle representing the phase dierence between E1 and E; remains at 90 then Eg1=Ep2, but when 0 becomes greater or less than 90 then E111 becomes less or greater than En. In Figure 1b, for example, the phase diierence between E3 and E1 is less than 90 and it will be seen that E111 is greater than En.

These principles are applied in the circuit of Figure 3, which consists basically of a phase detector tube I0, four gas tubes I2, I4, I8 and I8 and their associated circuits. The phase detector I0 includes identical amplifiers I and 2 with a common heater and connected cathodes 22a, 22h, and is shown as a twin pentode which may be of RCA Type 1644. The two anodes 24a, 2lb are connected by the primary winding 26 of an output transformer 28, and a center tap on this winding is connected to a terminal 30 at which 9 011111118. (cl. 31e- 28) direct current potential for the anode and screen grids of the amplifiers is applied.

The signal E1, one of the signals whose relative phase is to be controlled, is applied to terminal 2|, that is, between the control grid 32a of amplifier I and ground through a, capacitor 34a, and the signal E3, the other signal whose phase is to be controlled with respect to the first signal E1, is applied to terminal 25, that is, between the connected cathodes 22a, 22h and ground through a capacitor 36. The potential of the grid 32a-of amplifier I, with respect to its cathode 22a, varies in accordance with the vector sum of E1 and E3 and may, therefore, be represented by the vector E31 of Figure 1.

The signal E2 is derived in any conventional manner from a reference voltage which will produce the required phase and amplitude relation with respect to E1. This may be accomplished either by deriving E2 from E1 by means of a phase inverter, or both signals E1 and E2 may vbe derived from some other voltage Eo, as for example, by means of a center-tapped coil 82 coupled to a winding across which the voltage Eo is available, as shown in Fig. 2. The signal E2 is applied to the control grid 32h of amplifier 2 from terminal 23 through a capacitor 34h. Since E: has been applied to the connected cathodes, the potential of grid 32h with respect to its cathode 22h varies as the vector sum of Ez and Ea and may be represented by the vector Egz.

An alternating voltage is applied to and amplified by each amplier. This voltage may be from the commercial supply with a frequency of I sixty cycles per second and may be taken from the same source as the current for the heater 20. It is applied between a terminal 38 and ground' through a variable resistor 40 common to both units, and then to grid 32a through resistors 42a, 44a, and to grid 32h through resistors 42h, 44h of equal value with 42a, 44a. The two resistors 42a, 2b and the connection from the tap on the resistor 40 are joined at a terminal B0; the free terminals of the resistors 42a, 42h being connected to limit switches (not shown) by means of terminals 16, 18.

A resistor i4 connects the two grids 32a, 32h. This resistor is tapped, the tap being connected to the common heater 20 and to ground. If, owing to non-linearity of components or for some other reason, the gain of ampliiiers I and' 2 is not equal, the inequality may be compensated by adjustment of the tap on resistor 14.

We have seen that Eg1=Eq2 when E1 is in quadrature with E3. In that event, the alternating V 0 or 180 relation The phase displacement, with respect to the reference voltage, will be leading or lagging according to the nature of the detuning. A'control system based on this phase displacement for returning the circuit to exact resonance is much more sensitive than that which can be obtained by tuning the circuit to minimum plate current. It is therefore a further object of this invention to control the tuning of a power amplifier by comparing the phase of a voltage derived from and having a fixed phasal relation with respect to the amplifier tank voltage and a reference voltage obtained from a preceding ampliiier stage or vthe oscillator. One of the two voltages which are to be compared will be shifted in phase by 90 by conventional means. The two voltages will then normally have a quadrature phase relation and may be considered as the signals E1 and E: and applied to the phase responsive circuit of Fig. 3 as described above.

Figure 2 shows in block an intermediate power amplifier 8l and a power amplifier 86 of a transmitter. The two signals E1 and En are derived from the voltage Eo across the tank circuit of the intermediate power amplifier by the phase inverter center tapped transformer 82, and E: is a derived voltage which is in phase quadrature with the voltage across the inductor in the tank circuit of the succeeding stage. The 90 phase shift is obtained by connecting a capacitor 29 and a resistor 2i across the tank coil. Signal Ea is developed across the resistor, as is well known, and is available at terminal 25. l

The sensitivity of the device may be varied by adjustment of the variable resistor 40 which determines the amount of alternating voltage applied to the grids of the two amplifier units.

While E: need not be equal in magnitude to E1. it will be seen from Figure 1 that the circuit of the invention has maximum sensitivity when E: is of the same order of magnitude as E1 because then any departure from phase quadrature between these two signals causes maximum variation between Egi and En.

In motor control systems of the prior art the gas tubes conduct during only the positive half cycles of anode voltage, producing a wave of somewhat square shape. To round off the corners of this square-shaped wave, transformers have been conventionally connected between the gas tubes and the motor windings. The present system is more eiiicient electrically because the circuit produces a full wave of energizing current for the motor, the torque of the motor is instantly realized and the expense, weight and bulk of transformers is eliminated.

Part of the subject matter of the present application is disclosed in our copending application Ser. No. 570,706 for an Electronic Relay, filed concurrently herewith.

Since the balance of current in transformer 28 will be upset by a change in the phase of E3 with respect to Ei or by a change in the amplification of one of the two amplifiers I or 2, it follows that the system can be adjusted to respond to a phasal relation between E1 and E3 other than 90 by increasing the gain of one of the amplifiers. The system would then be balanced for that phase angle between E1 and Ea which would produce vectors En and En of such amplitudes that the resultant currents in the primary 26 would be equal.

There has thus been described a phase control system comprising a phase detector and motor control system. In the phase detector, a

balance is maintained between a pair of alternating current when two signals are in phase quadrature and an unbalance of these currents in either direction is caused to ignite one of two pairs of gas tubes whereby to produce a full wave of alternating energy for correcting the condition causing the unbalance.

We claim as our invention:

1. A phase responsive device comprising the combination of a circuit for deriving a pair of balanced alternating voltages from two signals having a predetermined phasal relation to each other, and a network responsive to an unbalance in said voltages for producing a full wave of alternating current, said network being constituted by a circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as one of the voltages of said pair and by another circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as the other of the voltages of said pair.

l2. A phase control comprising the combination of a circuit for deriving a pair of balanced alternating voltages from two signals in phase quadrature, and a network responsive to an unbalance in said voltages for producing a full wave of alternating current, said network being constituted by a circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as one of the voltages of said pair and by another circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as the other of the voltages of said pair.

3. A phase control comprising the combination of a circuit for deriving a pair of balanced alternating voltages from two signals in phase quadrature, a network responsive to an unbalance in said voltages for producing a full wave of alternating current, said network being constituted by a circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as one of the voltages of said pair and by another circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as the other` of the voltages of said pair, and apparatus actuated by said alternating current for returning said signals to phase quadrature.

4. A phase control comprising the combination of a circuit for deriving a pair of balanced alternating voltages from two signals in phase quadrature, a network responsive to an unbalance in said voltages for producing a full wave of alternating current, said network being constituted by a circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as one of the voltages of said pair and by another circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as the other of the voltages of said pair, and a motor actuated by said alternating current for returning said signals to phase quadrature.

5. A phase control comprising the combination of a circuit including a pair of amplifiers with a common cathode circuit for deriving a pair of balanced alternating voltages from two -signals in phase quadrature, and a network responsive to an unbaiance in said voltagesv for producing a full wave of alternating current, said network being constituted by a circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase as one of the voltages of said pair and by another circuit which includes two gas tubes energized by an alternating supply of the same frequency and phase vas the other of the voltages of said pair.

6. A phase control according to claim 5, characterized in that said common cathode circuit includes a variable resistor.

7. Apparatus for detecting a variation in phase relation between a first and second signal normally in quadrature, said apparatus comprising a pair of amplifiers of equal transconductance having common cathode circuits, each o! lsaid amplifiers having at least one control electrode inaddition to a cathode and an anode, an impedance connected between said anodes, means for obtaining a third signal of equal instantaneous absolute magnitude with said first signal and of opposite phase thereto, connections for applying said first and second signals between the control electrode and common cathode of one of said ampliiers and for applying said second y and third signals between the control electrode and common cathode of the other of said ampliners, connections for applying an alternating voltage to said common cathode circuit, and means responsive to the resultant voltage across said impedance.

8. A phase control comprising the combination of a circuit for deriving a pair of balanced alternating voltages from two signals in phase quadrature, and a network responsive to an unbalance in said voltages for producing a full wave of alternating current, said network being constituted s by a iirst circuit which includes two las tubes energized by an alternating supply of the same frequency and phase as one of the voltages of said ypair and by another circuit which includes -two gas tubes energized by an alternating supply of the same frequency and phase as the other of the voltages of said pair, each of said gas tubes having at least one control electrode in addition to a cathode and an anode, and the anode o! one of said tubes in each oi the circuits constituting said network being connected to the control electrode of the other tube in the same circuit.

9. A phase control according to claim 8, characterized in that each of the before-mentioned connections from the anode of one gas tube to the control electrode oi the gas tube in the same circuit includes a time delay combination.

J. G. BEARD.

ROBERT W. HARRALSON. ALEXANDER. KREITHEN.

REFERENCES CITED The following references are of record in the 

